Fix Windows build failing due to missing std::mutex

Author: nurupo

other/docker/windows/get_packages.sh

@@ -25,12 +25,16 @@ if [ "$SUPPORT_ARCH_i686" = "true" ]; then
   apt-get install -y \
     g++-mingw-w64-i686 \
     gcc-mingw-w64-i686
+  update-alternatives --set i686-w64-mingw32-gcc /usr/bin/i686-w64-mingw32-gcc-posix
+  update-alternatives --set i686-w64-mingw32-g++ /usr/bin/i686-w64-mingw32-g++-posix
 fi
 
 if [ "$SUPPORT_ARCH_x86_64" = "true" ]; then
   apt-get install -y \
     g++-mingw-w64-x86-64 \
     gcc-mingw-w64-x86-64
+  update-alternatives --set x86_64-w64-mingw32-gcc /usr/bin/x86_64-w64-mingw32-gcc-posix
+  update-alternatives --set x86_64-w64-mingw32-g++ /usr/bin/x86_64-w64-mingw32-g++-posix
 fi
 
 # Packages needed for running toxcore tests